The present invention relates to a coin selection apparatus used in an automatic vending machine or a money changing machine.
Various coin selection apparatus have been proposed. In one electronic coin selection apparatus, at least two detection coils are arranged in a path of coins and changes of impedances of the detection coils caused when a coin passes therethrough under an influence of electromagnetic fields by the detection coils are detected.
The selection system of the apparatus of this type includes a frequency change detection system in which the detection coils are used as oscillation coils and the changes of equivalent inductances caused when the coin passes therethrough are detected as changes of oscillation frequencies, an impedance voltage detection system in which the detection coils are used as oscillation coils and changes of equivalent loss resistances R caused when the coin passes therethrough are detected as changes of resonance circuit impedances, and a system in which a bridge circuit is constructed by the detection coil, a standard impedance element and two other impedance elements and a balance point of the bridge when the coin passes therethrough is detected.
In the coin selection, in order to enhance the selection accuracy including the selection of denomination of the coin and ejection of false coins, the above selection systems are combined, or in a single selection system, a plurality of frequencies are set for electromagnetic fields by the detection coils.
FIG. 8 shows a configuration of a prior art frequency change detection system. Three detection coils 201, 202 and 203 arranged in a coin path detect shape, thickness and material of a coin, respectively.
The detection coils 201, 202 and 203 are constructed as oscillation coils of oscillation circuits 204, 205 and 206 having independent oscillation frequencies. Numeral 207 denotes an AND circuit, and numeral 208 denotes a counter. The oscillation frequencies of the oscillation circuits 204, 205 and 206 are sequentially read by strobe signals S.sub.1, S.sub.2 and S.sub.3 from a microcomputer 209 and coins are selected by examining the read data by executing a coin selection program in the microcomputer 209. (See Japanese Examined Patent Publication No. 58-6985). In FIG. 8, IN.sub.A and IN.sub.B denote counter input ports.
FIG. 9 shows a configuration of a prior art bridge balance point detection system. An oscillation coil 351 is excited by an A.C. power supply 350 of a constant voltage and supplies constant voltages to two receiving coils 352 and 353. Numeral 310A denotes a detection coil for detecting material and thickness of a coin, and numeral 310B denotes a detection coil for detecting a shape of the coin. The detection coil 310A forms bridge circuits 311A-314A one for each denomination of coin and each including the detection coil 310A in one side of the bridge. Outputs of the bridge circuits are supplied to differential amplifiers 301A-304A, respectively, and outputs thereof are supplied to comparators 305A-308A, respectively. Outputs of the comparators 305A-308A are supplied to a discrimination circuit 309. The detection coil 310B is similarly configured to the detection coil 310A and connected to the discrimination circuit 309.
An output of the A.C. power supply of the bridge circuits is supplied to the discrimination circuit 309 through a waveform conversion circuit 310.
The discrimination circuit 309 supplies a reference pulse train to a clock pulse input port CP and output levels from the comparators 305A-308A and 305B-308B and compares them with a predetermined reference to select the coin. (See Japanese Examined Patent Publication No. 58-30632).
In FIG. 9, L1A-L4A and R1A-R4A are variable inductors and variable resistors which form standard impedance elements for denominations of coins of the bridge circuits 311A-314A including the detection coil 310A, Y.sub.0A -Y.sub.4A are one-side impedances of the bridge circuits 311A-314A, and L.sub.1B -L.sub.4B, R.sub.1B -R.sub.4B and Y.sub.0B -Y.sub.4B are variable inductors, variable resistors and impedances of the bridge circuits 311B-314B. IN.sub.1A -IN.sub.4A and IN.sub.1B -IN.sub.4B denote input ports.
FIG. 10 shows a configuration of a prior art impedance voltage detection system. Numeral 901 denotes a detection coil arranged in a coin path to detect a material of a coin, numerals 902 and 903 denotes detection coils for detecting a thickness of the coin and numeral 904 denotes a detection coil for detecting a diameter of the coin. The coils 901-904 form a portion of an oscillation circuit OSC. Changes of impedances of the coils 901-904 are outputted as a frequency change of the oscillation circuit OSC and the frequency change is converted to a voltage by a frequency-voltage conversion circuit FVC, an output of which is supplied to material, thickness and diameter discrimination circuits M, T and D. The discrimination circuits M, T and D compare the detection outputs with predetermined references for each denomination of coin to select the coin. Numerals 905, 906 and 907 denote sensors arranged near the detection coils 901, 902 and 903, respectively, for detecting passage of the coin through the detection coils. The discrimination circuits M, T and D are set and reset by the signals of the sensors 905, 906 and 907. (See Japanese Examined Utility Model Publication No. 56-11182). A.sub.1 -A.sub.4 denote AND gates which produce outputs when coins A, B, C and D are discriminated, respectively, and A.sub.5 denotes an AND gate which produces a false coin output when a coin does not correspond to any of the coins A, B, C and D. The AND gate A.sub.5 produces the output when NO signals are supplied from the discrimination circuits M, T and D. DT.sub.1 and DT.sub.2 denote first and second differentiation circuits which output signals in response to the detection signals of the passage deteotion sensors 905 and 907. A flip-flop FF is set and reset by those signals.
In the prior art selection apparatus shown in FIG. 8, a plurality of independent oscillation circuits are provided one for each of test items of the coin (size, material and thickness) and they are operated at the frequencies suitable for the respective tests. As a result, the flows of signals in the detection system is complex and the circuit configuration is complex. Further, wiring cables for the detection coils must be shielded in order to prevent interference of the signals in the oscillation circuits.
In the circuit of FIG. 9, two-side bridge impedance elements, differential amplifier and comparator are required for one detection coil for each denomination of coin. Thus, the signal flows in the detection system is complex and a number of circuit components are required. Further, adjustment for balancing the bridge for each denomination of coin is required.
In the circuit of FIG. 10, the detection coils are connected in series and the detection circuit including the oscillation circuits is simplified. However, the independent detection coils are required one for each of the test items of the coin (size, material and thickness), and the coin passage sensor and the detection circuit are required for each detection coil. Accordingly, the number of circuit components increases and the circuit configuration is complex.
The prior art selection apparatus are thus complex in the circuit configuration and require a large number of components. Accordingly, the cost increases, chance of occurrence of trouble is high and serviceability is low because the signals in the detection system are complex.
In a coin changer or an automatic vending machine which incorporates the coin selection apparatus, a demand to reduce the size of the apparatus has been increasing. The prior art apparatus cannot satisfy such demand.